Home-made explosives: the facts

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Acetone peroxide - TATP, or Mother of Satan as it is known, due to its devastating effects - is the home-made explosive that police believe was used by the London bombers. Anyone with a basic knowledge of chemistry can make it.

The confirmation of the type of explosive involved is a crucial part of the investigation into the bomb plot. It is made using commonly available chemicals such as sulphuric acid, which is used to clean drains, hydrogen peroxide, which is used in hair dyes, and acetone. The process involves evaporating the liquid, leaving behind crystals that constitute the explosive, which may explain why a large quantity was found in a bath at a property used by the bombers.

However, it is highly unstable, being sensitive to heat, friction and shock - even professionals have been injured while using it.

What remains unclear is whether the white crystals were "plasticised'' a process which turns the material into something more resembling plastic explosive, and therefore less volatile. This may have been to ensure the bombs did not detonate early and could explain initial reports that the explosives were "military style".

Andy Oppenheimer, an expert on explosives and terrorism for Jane's Defence Weekly, said: "Anyone can make acetone peroxide - at the risk of losing their fingers - but it is very, very volatile.'' Because of that, he said, the evidence still pointed towards outside assistance for the bombers.

There is a precedent for the use of TATP in Islamic terrorism. In 2001 the British-born ''shoe bomber'' Richard Reid, tried to blow up an airline with plasticised TATP.